Turns out GaussianConditional-inl.h was needed after all

gtsam/linear/GaussianConditional-inl.h

@@ -0,0 +1,48 @@
+/* ----------------------------------------------------------------------------
+
+ * GTSAM Copyright 2010, Georgia Tech Research Corporation, 
+ * Atlanta, Georgia 30332-0415
+ * All Rights Reserved
+ * Authors: Frank Dellaert, et al. (see THANKS for the full author list)
+
+ * See LICENSE for the license information
+
+ * -------------------------------------------------------------------------- */
+
+/**
+ * @file    GaussianConditional-inl.h
+ * @brief   Conditional Gaussian Base class
+ * @author  Christian Potthast
+ */
+
+// \callgraph
+
+#pragma once
+
+#include <boost/range/join.hpp>
+#include <boost/assign/list_of.hpp>
+
+namespace gtsam {
+
+  /* ************************************************************************* */
+  template<class PARENTS>
+  GaussianConditional::GaussianConditional(Index key, const Vector& d,
+    const Matrix& R, const PARENTS& parents, const SharedDiagonal& sigmas, const typename PARENTS::value_type*) :
+  BaseFactor(boost::join(
+    boost::assign::cref_list_of<1,typename PARENTS::value_type>(std::make_pair(key, R)),
+    parents), d, sigmas),
+    BaseConditional(1) {}
+
+  /* ************************************************************************* */
+  template<typename TERMS>
+  GaussianConditional::GaussianConditional(const TERMS& terms,
+    size_t nrFrontals, const Vector& d, const SharedDiagonal& sigmas) :
+  BaseFactor(terms, d, sigmas), BaseConditional(nrFrontals) {}
+
+  /* ************************************************************************* */
+  template<typename KEYS>
+  GaussianConditional::GaussianConditional(
+    const KEYS& keys, size_t nrFrontals, const VerticalBlockMatrix& augmentedMatrix, const SharedDiagonal& sigmas) :
+  BaseFactor(keys, augmentedMatrix, sigmas), BaseConditional(nrFrontals) {}
+
+} // gtsam

gtsam/linear/GaussianConditional.h

@@ -152,3 +152,5 @@ namespace gtsam {
 
 } // gtsam
 
+#include <gtsam/linear/GaussianConditional-inl.h>
+